Printer

ABSTRACT

The object is to provide a printing apparatus wherein the rotation of endless printing bands is limited in a manner that keeps excessive rotational force from acting on the endless printing bands 7 themselves, thereby avoiding wear, cracking and other damage, and wherein forcible rotation of the endless printing bands causes idle rotation of selector wheels 5 and puts only moderate load on the endless printing bands. Attention is directed to adoption of selector wheel 5 rotation restricting members of a movable type and to enabling the movable stop members 14 to move when excessive force acts on the selector wheels 5 or the endless printing bands 5. A stop bearing member 15 is provided to abut on elastic sections 14B of the movable stop members 14, and engagement between drive projections 7E and the elastic sections 14B with movement of the endless printing bands 7 enables movement of the movable stop members 14.

TECHNICAL FIELD

This invention relates to a printing apparatus, particularly to a devicefor preventing display character fouling in a printing apparatusinstalled in portable label printing and affixing apparatus (handlabeler) or the like.

BACKGROUND ART

The printing apparatus of a hand labeler generally has selector wheelssupported on a shaft at one end portion of a printer frame and a typebearing member section at the other end portion of the frame. Endlessprinting bands made of a flexible material such as rubber or syntheticresin and formed on their outer surfaces with types and displaycharacters are wound around the selector wheels and the type bearingmember section. The selector wheels are rotated to rotate the endlessprinting bands to locate desired types on the outer surfaces of the typebearing member section where they can be printed, ink is applied to thetypes by an ink roller or the like, and the types can then be impressedon a label or the like.

Each endless printing belt is formed with types around one half itsperimeter and display characters around the other half of its perimeter,the arrangement being defined so that the display character at theposition viewable through a display window section provided in theprinter frame corresponds to the type positioned at the type bearingmember section.

Prescribed types can therefore be positioned at the type bearing membersection by using a type select operating shaft to rotate the selectorwheels while viewing the display characters through the display windowsection.

However, if an endless printing band is rotated beyond the prescribedrotation range when it is rotated by operating the type select operatingshaft, the display characters may be rotated as far as the type bearingmember section and be fouled by application of ink thereto by the inkroller. This leads to such problems as that the display charactersbecome hard to see when selecting prescribed types while viewing thedisplay characters through the display window section.

Various proposals have been made for preventing this fouling of thedisplay characters (by ink application prevention means). In the"printing band structure" of Japanese Patent Publication No. Sho62(1987)-33080, for example, a projection is provided on a rotating diskfor rotating the endless printing band and a stop is provided in thevicinity of the rotation range region of the endless printing band.Owing to abutment of the projection on the stop, the rotating disk canrotate only within the prescribed region.

However, this device involves problems such as that the projectioninterferes with the display characters and that if the rotating disk isrotated with excessive force after the projection strikes on the stop,the endless printing band may elongate, causing it to print improperlyor fall off.

Further, in the "printer" of Japanese Patent Application Laid-open No.Hei 6(1994)-155878, a protuberance is formed on the outer peripheralsurface of the endless printing band to be engageable with a stop andthe crest surface of a drive projection engaging with an indentationprovided on the periphery of the selector wheel is formed as a slantedsurface. When a selector wheel is forcibly rotated after the endlessprinting band has reached the limit position, the endless printing bandslips.

In this printing apparatus, however, the problem arises that theslipping at the time the endless printing band is rotated with excessiveforce wears, cracks and otherwise damages the slanted surface of theendless printing band.

Moreover, since the outer peripheral surface of the endless printingband is formed with the protuberance, the problem arises that the numberof type that can be provided on the endless printing band decreases.

Further, in the "device for preventing fouling of printer displaycharacters" of Japanese Utility Model Application Laid-open No.6(1994)-71146, the rotation range of the endless printing band islimited by abutment of a sectionally thick type portion formed on theouter perimeter of the endless printing band with a leg portion of anindicator.

Damage of the indicator and damage of the endless printing band bycracking and the like when excessive rotational force are also a problemin this device. Another problem is that the endless printing band maypass beneath the indicator.

In "printer" of Japanese Patent Publication No. Hei 4(1992)-34951, onthe other hand, rotation of the endless printing band is limited byengagement between a tooth formed on the endless printing band and astop shoulder.

This printing apparatus also has problems in that application ofexcessive rotational force elongates the endless printing band andcauses wear, cracking and other damage.

Thus in all of these configurations the attempt to prevent fouling ofthe display characters by limiting rotation of the endless printing bandto a prescribed region makes it difficult to avoid the direct orindirect action of large external forces on the endless printing band.They therefore encounter the problems of elongation and damage, theproblem that the original purpose cannot be achieved because theprojections ride over the stops, and other problems.

This invention was accomplished in the light of the aforesaid problemsand has as an object to provide a printing apparatus which preventsfouling of the display characters on an endless printing band by keepingthem from being positioned at the type bearing member section, i.e.,from being brought opposite the ink roller.

Another object of the invention is to provide a prnting apparatuswherein the rotation of an endless printing band is limited in a mannerthat keeps excessive rotational force from acting on the endlessprinting band itself, thereby avoiding wear, cracking and other damage.

Another object of the invention is to provide a printing apparatus whichminimizes the reduction in number of type caused by formation of aprojection for limiting rotation of an endless printing band.

Another object of this invention is to provide a printing apparatuswherein forcible rotation of an endless printing band at its rotationlimit causes idle rotation of the selector wheel and puts only moderateload on the endless printing band.

Another object of this invention is to provide a printing apparatuswherein the tension (degree of tautness) of an endless printing band canbe regulated within a prescribed range.

DISCLOSURE OF THE INVENTION

A first aspect of the invention is directed to enabling idle rotation ofthe selector wheels by adopting selector wheel rotation restrictingmembers (movable stop members) of a movable type having elasticsections, enabling the movable stop members to move when excessive forceacts on the selector wheels or the endless printing bands, and allowingthe engaged state of the endless printing bands with the selector wheelsto become a partially engaged state therewith to produce slack.According to this first aspect of the invention, a printer having atleast one endless printing band formed on its outer peripheral surfacewith multiple types and display characters and wound about a selectorwheel and a type bearing member section and enabling selection of adesired type of the endless printing band is characterized in comprisinga movable stop member provided between the selector wheel and the typebearing member section and formed at one end portion with at least oneregulating boss portion for engaging the selector wheel and provided atanother end portion thereof with an elastic section having at least oneengagement piece, a stop bearing member for restricting movement of themovable stop member by abutting on the elastic section of the movablestop member, and at least one drive projection provided on an innerperipheral surface of the endless printing band to be engageable withthe engagement piece of the elastic section of the movable stop member,engagement between the drive projection and the engagement piece withmovement of the endless printing band causing movement of the movablestop member to enable release of the engagement between the selectorwheel and the regulating boss section.

To stabilize the moving action of the movable stop member, the printercan be provided with a stop guide for guiding the movable stop member inits movement direction.

The elastic section can have a bifurcated engagement spring section.Since the bifurcated engagement spring section can elastically deformlaterally with movement of the movable stop member in the verticaldirection, for example, the engagement between the drive projection ofthe endless printing band and the elastic section can be furtherstrengthened and the movable stop member can effect smooth elasticmovement.

The stop bearing member can have a slanted bearing surface for bearingthe elastic section. Since the elastic section is elastically deformedalong the slanted bearing surface when the movable stop member moves,the engagement between the drive projection of the endless printing bandand the elastic section can be further strengthened and the movable stopmember can effect smooth elastic movement.

The endless printing band can have at least one blank section with notypes on its peripheral surface and the inner peripheral surface atleast one display character adjacent to the side of the blank section inthe direction of rotation can be made a flat section.

Specifically, the inner peripheral surface at least one displaycharacter adjacent to the side of the blank section in the direction ofrotation can be formed without projections capable of engaging with theselector wheel, thereby avoiding engagement between the selector wheeland the endless printing band and facilitating idle rotation of theselector wheel.

According to a second aspect of the invention, a printing apparatushaving at least one endless printing band formed on its outer peripheralsurface with multiple types and display characters and wound about aselector wheel and a type bearing member section and enabling selectionof a desired type of the endless printing band is characterized incomprising a stop member provided between the selector wheel and thetype bearing member section and at least one drive projection providedon an inner peripheral surface of the endless printing band to beengageable with the stop member, engagement between the drive projectionand the stop member with movement of the endless printing band producingslack in the endless printing band to enable idle rotation of theselector wheel.

In the device for preventing display character fouling in a printeraccording to this invention, the regulating boss portion and the elasticsection are formed on the movable stop member, the regulating bossportion engages with the selector wheel, and the elastic sectionelastically deforms. As a result, regulation of the endless printingband type selection operation (appropriate set states of individualtypes at the type bearing member section and differentiation of the setstates) can be secured.

Therefore, while types and display characters of the endless printingband can be selected as desired by rotating the selector wheel to rotatethe endless printing band thereabout, a drive projection of the endlessprinting band engages with the elastic section of the movable stopmember just before a display character strikes (contacts) the ink rollerto produce a sensation of resistance (resistance action) tending to oncehalt the rotation.

When an attempt is made to rotate the selector wheel beyond the point ofthis resistance action, the elastic section elastically deforms and themovable stop member itself moves slightly toward the type bearing membersection side.

In this way, the rotational traction between the regulating boss portionof the movable stop member and the selector wheel decreases below thatin the normal type selection state and, in addition, the endlessprinting band slackens from its engagement point with the selector wheelto its engagement point with the elastic section of the driveprojection, thereby releasing its engagement with the selector wheel andallowing the selector wheel to rotate idly.

Since the display characters are therefore not rotated to and positionedat the rotation region of the ink roller, fouling thereof can beprevented. Moreover, any excessive force acting to rotate the selectorwheel further is transferred through the endless printing band and adrive projection thereof to the elastic section of the movable stopmember, whereafter it acts in the direction of producing idle rotationbetween the regulating boss portion of the movable stop member and theselector wheel and does not damage the endless printing band.

Since the drive projection is provided on the inner peripheral surfaceof the endless printing band and made engageable with the elasticsection of the movable stop member, there is no reduction of the numbersof types and display characters on the peripheral surface of the endlessprinting band.

In the second aspect of the invention, slack is produced in the endlessprinting band when its rotation is prevented by its engagement with thestop member, the selector wheel and the endless printing band are put ina released state or in a state in which, even if they contact, rotationof the selector wheel does not act on the endless printing band, theselector wheel rotates idly, the endless printing band does not move tomove the display characters as far as the type bearing member section,and the possibility of the display characters being fouled by contactwith the ink roller is eliminated.

A third aspect of the invention is characterized in that a cam memberwhose rotational position can be adjusted is provided within the endlessprinting band to be rotatable into and out of contact with the innerperipheral surface of the endless printing band. In this case, thetension of the endless printing band can be adjusted by rotating the cammember to vary the degree of contact between the cam member and theendless printing band.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a printer according to the first aspect ofthe invention;

FIG. 2 is a sectional view taken along line II--II in FIG. 1;

FIG. 3 is a sectional view showing an endless printing band of theprinter shown in FIG. 1 when rotated to the rotation-prevented state;

FIG. 4 is a sectional view showing the idle rotation state of a selectorwheel;

FIG. 5 is sectional view of a printer according to the second aspect ofthe invention;

FIG. 6 is a sectional view taken along line VI--VI in FIG. 5;

FIG. 7 is a side view of an endless printing band in the second aspect;

FIG. 8 is a sectional view showing the rotation-prevented state ofendless printing bands and the idle rotation state of selector wheels;

FIG. 9 is a sectional view of a printer according to the third aspect ofthe invention;

FIG. 10 is a sectional view taken along line II--II in FIG. 9;

FIG. 11 is a side view of an adjuster;

FIG. 12 is a partially cut-away enlarged side view of an essentialportion of a printer frame and an adjuster section;

FIG. 13 is a sectional view showing an endless printing band of theprinter shown in FIG. 9 when rotated to the rotation-prevented state;and

FIG. 14 is sectional view showing the idle rotation state of a selectorwheel.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIGS. 1 and 2, one end portion of a printer frame 3 of a printer 1 isprovided with multiple selector wheels 5 which are selectively rotatableby an operating shaft 4 for type selection, the other end portionthereof is provided with a type bearing member section 6 of T shapesection extending parallel to the operating shaft 4 for type selection,and endless printing bands 7 are wound about the selector wheels 5 andthe type bearing member section 6 under prescribed tension. That is,multiple rows of the endless printing bands 7 are wound about theselector wheels 5 and the type bearing member section 6.

A display window 8 is formed as an opening in the printing apparatusframe 3 at an end surface portion thereof facing the selector wheels 5and the end surface portion provided with the type bearing membersection 6 is formed with an ink roller access opening 9. An ink roller Rcan move into contact with the endless printing bands 7 at the inkroller access opening 9.

The operating shaft 4 is used to select specific types of the endlessprinting bands 7 by moving it in the axial direction to select (locate)a desired row of the endless printing bands 7 and rotating the selectorwheel 5 of the located row. The operating shaft is mounted with respectto the printing apparatus frame 3 to be movable in the direction of itsaxis and to be rotatable about its axis. Its outer peripheral surface isformed with multiple locator grooves 4A spaced regularly in the axialdirection and a rotary pin 11 is formed to project for near its tip.

On the other hand, the printing apparatus frame 3 is formed with avertical hole 3A for accommodating a steel locator ball 12 and the steellocator ball 12 accommodated in the vertical hole 3A is urged toward thelocator grooves 4A by a locator spring 13 to engage the steel locatorball 12 with one of the locator grooves 4A.

Thus when the operating shaft 4 is moved axially, the steel locator ball12 successively engages with the locator grooves 4A. At this time, therotary pin 11 successively moves to the positions of correspondingselector wheels 5 to engage with internal engagement recesses 5A formedat the inner peripheral surfaces of the selector wheels 5. Thus theselector wheel 5 of the desired row can be located by axially moving theoperating shaft 4.

The printer frame 3 is further equipped with an indicator 10 movablealong the display window 8 in parallel with the axis of the operatingshaft 4. The indicator 10 is connected to the operating shaft 4 to beonly rotatable relative thereto and to move integrally with theoperating shaft 4 in the axial direction. The indicator 10 is formedwith a pointer 10A which projects into the display window 8. The pointer10A points to the selector wheel 5 of the desired row selected by theoperating shaft 4.

Each endless printing band 7 is formed at separate regions on its outerperipheral surface with prescribed numbers of types 7A and displaycharacters 7B. Specifically, half of the outer periphery of each endlessprinting band 7 is formed with a plurality of types 7A and the otherhalf of the outer periphery thereof is formed with a plurality ofdisplay characters 7B. A blank section 7C is formed at each boundaryregion between the group of types and the group of display charactersand, as explained later, the blank sections 7C face the display window 8and the ink roller access opening 9 when the endless printing band 7 isat the terminal portion of its movement range.

The portion of the inner peripheral surface of the endless printing band7 opposite the types 7A is made flat and the portion thereof oppositethe display characters 7B is formed with low drive projections 7D andhigh drive projections 7E each engageable with peripheral engagementnotches 5B of the selector wheel 5.

The high drive projections 7E are provided at portions opposite displaycharacters 7B located substantially in the middle of the plurality ofdisplay characters 7B. The number thereof can be freely set in light ofthe numbers of the types 7A and the display characters 7B and the liketo extend over a prescribed region on the inner peripheral surface ofthe endless printing band 7.

When the selector wheel 5 is rotated, the low drive projections 7D andthe high drive projections 7E engage with the peripheral engagementnotches 5B of the selector wheel 5 to rotate the endless printing band 7and enable a desired type 7A to contact the ink roller R at the inkroller access opening 9.

Plural movable stop members 14 associated with the respective selectorwheels 5 are mounted on the printing apparatus frame 3 between theselector wheels 5 and the type bearing member section 6 and inside theendless printing bands 7 wound about the selector wheels 5 and the typebearing member section 6.

Specifically, a stop guide 3B is provided to project from the printingapparatus frame 3 and this stop guide 3B fits into elongate guidewindows 14C formed at the center portions of the movable stop members14. The movable stop members 14 can move to some degree in thedirections of approaching and separating from the selector wheels 5.

Each movable stop member 14 is formed at one end with a pair ofregulating boss portions 14A for engaging the peripheral engagementnotches 5B of the selector wheel 5 and at the other end thereof with anelastic section 14B.

The elastic section 14B has a bifurcated engagement spring section 14D.The bifurcated engagement spring section 14D is formed at its tipportion with outward projecting engagement pieces 14E. The tip surfacesof engagement pieces 14E are formed as slanted surfaces 14F that splaytoward the tip end. A stop bearing member 15 is disposed between themovable stop members 14 and the type bearing member section 6. As shownin FIG. 2, the stop bearing member 15 is formed integrally with theprinting apparatus frame 3. The surfaces of the stop bearing member 15facing the movable stop members 14 are formed as bearing member sideslanted surfaces 15A which abut on the slanted surfaces 14F of theengagement pieces 14E. The movement of the movable stop members 14 isrestricted by the abutment of the slanted surfaces 14F and the bearingmember side slanted surfaces 15A.

In the normal selectable state, the movable stop members 14 areindividually urged toward the selector wheels 5 by the action of theelastic sections 14B. An upper gap S1 is formed between the elongateguide windows 14C and the stop guide 3B so that the movable stop members14 can move downward in the drawings and also return.

The printing apparatus frame 3 is provided between the selector wheels 5and the type bearing member section 6 with presser frames 3C, 3D forpreventing outward deviation of the endless printing bands 7. As shownin FIGS. 1 and 2, in the normal type selectable state of the printingapparatus 1 configured in this manner, a desired row can be selected bymoving the operating shaft 4 in the axial direction, whereafter adesired type 7A can be selected by rotating the operating shaft 4 eitherclockwise or counterclockwise at that row so as to rotate the endlessprinting band 7 via the selector wheel 5 and stopping the rotation ofthe operating shaft 4 at the position where the desired displaycharacter 7B of the endless printing band 7 can be seen through thedisplay window 8.

In this selected state, the type 7A corresponding to the selecteddisplay character 7B is set on the type bearing member section 6 andexposed at the ink roller access opening 9. Printing can be effected byturning the ink roller R to apply ink to this type 7A and pressing thewhole printing appratus 1 onto a label by, for example, operating a handlever (not shown) or the like.

FIG. 3 is a sectional view showing an endless printing band 7 whenrotated clockwise in the drawing to the rotation-prevented state. Thisis an example where the operating shaft 4 was operated to rotate theselector wheel 5 until the endless printing band 7 rotated clockwise byan amount causing the blank sections 7C to come opposite the displaywindow 8 and the ink roller access opening 9 and a high drive projection7E of the endless printing band 7 to engage with one engagement piece14E (right side of the drawing) of the elastic section 14B of themovable stop member 14.

The engagement between the high drive projection 7E and the engagementpiece 14E therefore prevents the selector wheel 5 from rotating even ifan attempt is made to rotate the selector wheel 5 further, wherebypositioning of display characters 7B of the endless printing band 7 atthe ink roller access opening 9 is avoided and fouling of displaycharacters 7B by the ink roller R is prevented.

FIG. 4 is a sectional view showing the idle rotation state of a selectorwheel 5. In the foregoing rotation-prevented state, if an attempt ismade to forcibly rotate the selector wheel 5 further, the peripheralengagement notches 5B of the selector wheel 5 escape from the regulatingboss portions 14A of the movable stop members 14 to ride thereon in theillustrated state.

Specifically, the movable stop member 14 moves downward in the drawingguided by the stop guide 3B, whereby a lower gap S2 occurs between theelongate guide window 14C and the stop guide 3B, the slanted surfaces14F of the elastic section slide on the bearing member side slantedsurfaces 15A, the legs of the bifurcated engagement spring section 14Dof the elastic section 14B spread laterally outward, and the engagementbetween the engagement piece 14E and the high drive projection 7E of theendless printing band 7 is strengthened.

In this state, the selector wheel 5 rotates idly because slack developsin the endless printing band 7 between the portion of the blank section7C on the upper side and the portion of the engagement piece 14E so thatthe low drive projections 7D escape from the peripheral engagementnotches 5B of the selector wheel 5.

Since the engagement portion between the engagement piece 14E and thehigh drive projection 7E is located downstream in the direction ofrotation of the selector wheel 5 and the endless printing band 7 and,further, the presser frames 3C and 3D restrain the endless printing band7 and keep it from bulging outward, the amount of slack developedbetween the selector wheel 5 and the endless printing band 7 issufficient to ensure idle rotation of the selector wheel 5.

The selector wheel 5 can therefore rotate idly when an excessiveexternal force acts thereon. Moreover, while the selector wheel 5rotation itself acts more on the regulating boss portions 14A of themovable stop member 14 than on the endless printing band 7, no hindranceto type selection arises owing to wear of the movable stop member 14since the movable stop member 14 is harder than the endless printingband 7.

If the selector wheel 5 is rotated in the opposite (counterclockwise)direction, the engagement between the peripheral engagement notches 5Band the regulating boss portions 14A is reestablished and the elasticityof the movable stop member 14 restores it to its original position shownin FIG. 1.

FIGS. 5 and 6 are sectional views of a dual printer 20 according to thesecond aspect of the invention. FIG. 6 is a sectional view taken alongline VI--VI in FIG. 5. The printer 20 is constituted by combining twoprinters 21 of substantially the same structure. Like portions to thoseof the printer 1 are assigned like reference symbols in the drawings andwill not be explained in detail. Only structural features differing fromthose of the printer 1 will be explained.

A first presser frame 23A and a second presser frame 23B of the printerframe 23 of the printer 20 are formed substantially laterallysymmetrical and a guide plate 24 is provided midway between them,thereby ensuring smooth movement of endless printing bands 7.

Sleeves 25 are fitted in the printer frame 23 to be rotatable abouttheir axes. Selector wheels 5 are supported on the sleeves 25 andoperating shafts 4 are inserted into the sleeves 25. The sleeves 25 areformed in the axial direction with slits 25A (FIG. 6). Rotary pins 11erected on the operating shafts 4 are inserted into the slits 25A andthe tips of the rotary pins 11 engage with internal engagement recesses5A of the selected selector wheels 5.

On the other hand, the operating shafts 4 are fitted with co-rotationprevention rods 26 rods for permitting rotation of only the selectedselector wheels 5. Each co-rotation prevention rod 26 is fitted on theassociated operating shaft 4 to be rotatable only in parallel with andrelative to the operating shaft. It is mounted to be movable relative tothe printing apparatus frame 23 only in its axial direction and engageswith a single peripheral engagement notch 5B of each associated selectorwheel 5. The co-rotation prevention rod 26 is formed at a locationfacing the rotary pin 11 with a notch 26A for permitting rotation of theselector wheel 5 engaged by the rotary pin 11.

Therefore, since only the specific selector wheel 5 selected by theoperating shaft 4 can rotate and the peripheral engagement notches 5B ofthe other selector wheels 5 are engaged with the co-rotation preventionrod 26, the selector wheels 5 adjacent to the specific selector wheel 5being rotated are prevented from rotating so that no endless printingband 7 other than the selected and operated endless printing band moves.

FIG. 7 is a side view of an endless printing band 7. The number of lowdrive projections 7D formed on the inner peripheral surface of theendless printing band 7 is two less than in the case of the printingapparatus 1 (FIG. 1).

Specifically, the inner peripheral surface portions at the displaycharacters 7B adjacent to the blank sections 7C on the downstream sidethereof in the direction of rotation of the endless printing band 7 arenot formed with low drive projections 7D but are formed as flat portions7F.

Although the illustrated example shows a pair (two) of flat portions 7Fon the inner peripheral surface of the endless printing band 7, insofaras the ability to rotationally drive the endless printing band 7 by theselector wheel 5 can be maintained, it is possible to further facilitatethe occurrence of idle rotation by providing the inner peripheralsurface of the endless printing band 7 with two sets of two side-by-sideflat portions 7F (total of four).

Since the dual printer 20 of this configuration provides the sameeffects as that shown in FIG. 1 and other figures, in can reliablyprevent fouling of the display characters 7B by the ink roller R withoutdamaging the endless printing bands 7.

Specifically, as shown in FIG. 8, taking the printer 21 on the rightside by way of example, when a high drive projection 7E of the endlessprinting band 7 engages one of the engagement pieces 14E of the movablestop member 14 owing to rotation of the selector wheel 5 in theclockwise direction, further rotation of the selector wheel 5 isprevented (rotation-prevented state).

If the selector wheel 5 of the printing apparatus 21 on the right sideof FIG. 8 is rotated clockwise in an attempt to cause further clockwiserotation from the rotation-prevented state, the selector wheel 5 ridesup on the regulating boss portions 14A and assumes an idly rotatingstate owing to separation of the outer peripheral surface of theselector wheel 5 in the direction of rotation from the inner peripheralsurface of the endless printing band 7 including the flat portions 7F(with no drive projections). In other words, as is clear from thedrawings, the endless printing band 7 exhibits a slack state relative tothe selector wheel 5, giving rise to idle rotation.

To be more specific, since the inner peripheral surface at the displaycharacter 7B immediately to the right in the figure from the blanksection 7C positioned at the display window 8 is a flat portion 7F withno low drive projection 7D, engagement between the selector wheel 5 andthe endless printing band 7 easily releases, whereby slack tends todevelop in the endless printing band 7 to enable ready transition to theidle rotation state.

Since the other operations and effects are the same as those of thefirst aspect, they are not described in detail here.

Like the printer according to the second aspect described in theforegoing, that according to the first aspect shown in FIGS. 1 to 4 canalso be configured to facilitate the development of slack in the endlessprinting bands 7 so as to enable ready transition of the selector wheels5 to the idle rotation state.

When the diameter of the selector wheels 5 according to the first aspectare made smaller than the selector wheels according to the secondaspect, the development of slack in the endless printing bands 7 and thetransition of the selector wheels 5 to the idle rotation state can befacilitated by defining the height of the low drive projections 7D atpositions corresponding to the flat portions 7F to fall within aprescribed range.

Further, when these selector wheels 5 are larger than in the secondaspect (FIG. 5), the idle rotation state is readily exhibited if theflat portions 7F formed on the inner peripheral surfaces of the endlessprinting bands 7 are made equivalent to two characters to the left andright of the blank sections 7C.

FIGS. 9 and 10 are sectional views of a printing apparatus according tothe third aspect of the invention. A tension adjustment mechanism 30 forthe endless printing bands is disposed within the endless printing bands7 at a location between the stop bearing member 15 and the type bearingmember section 6. The tension adjustment mechanism 30 has an adjuster 31(cam member). As shown in FIG. 11, the adjuster 31 is integrally formedof a sectionally elliptical main body 31A, cam adjustment rotary shafts31B, an adjustment arm 31C and an engaging ridge 31D.

Specifically, the sectionally elliptical main body 31A is provided onopposite end surfaces with cam adjustment rotary shafts 31B. Thesectionally elliptical main body 31A is rotatably supported on theprinting apparatus frame 3 by the cam adjustment rotary shafts 31B. Whenthe sectionally elliptical main body 31A is rotated, its outerperipheral portion makes and breaks contact with the inner peripheralsurfaces of the endless printing bands 7.

One end surface of the sectionally elliptical main body 31A is formedwith the adjustment arm 31C extending perpendicular to the camadjustment rotary shaft 31B, and the engaging ridge 31D is provided onthe tip portion of the adjustment arm 31C to face the printer frame 3.

On the other hand, as shown in FIG. 12, a surface of the printer frame 3lying perpendicular to the drawing sheet is formed with multipleradially extending cam adjustment grooves 32 with which the engagingridge 31D can engage. Other points are the same as shown in FIGS. 1 and2.

At the time assembly of the printer at the factory, for example, theattitude or relative position of the sectionally elliptical main body31A with respect to the endless printing bands 7 can be adjusted byrotating the sectionally elliptical main body 31A about the camadjustment rotary shafts 31B to bring the engaging ridge 31D of theadjustment arm 31C into engagement with a desired one of the camadjustment grooves 32 of the printer frame 3.

As shown in FIG. 9, for example, the tension of the endless printingbands 7 can be increased by positioning the sectionally elliptical mainbody 31A to thrust toward the endless printing bands 7 since this causesthe sectionally elliptical main body 31A to abut relatively strongly onthe inner peripheral surfaces of the endless printing bands 7.

Otherwise, if the sectionally elliptical main body 31A is rotated to theattitude shown in FIGS. 13 and 14, the adjuster 31 does not contact theinner peripheral surfaces of the endless printing bands 7, whereby thetension of the endless printing bands 7 can be reduced.

Adjustment of the rotation angle of the adjuster 31 thus enablesadjustment of the tension of the endless printing bands 7 for ensuringtheir proper rotation and further enables the condition of slackening ofthe endless printing bands 7 in the idle rotation state shown in FIG. 14and the effect of the idle rotation of the selector wheel 5, which isrelated to the slackened condition, to be brought within the desiredranges.

The set angular position of the adjuster 31 can also be adjusted toreadjust the tension of the endless printing bands 7 in response toelongation or slackening of the endless printing bands 7 during use ofthe printing apparatus.

Since, as explained in the foregoing, the invention provides the stopmembers, each having regulating boss portions and an elastic section,and further provides the stopper bearing member on which the elasticsections abut to restrict movement of the movable stopper members, itenables the selector wheels to ride up and rotate idly, therebypreventing fouling of the endless printing bands by the ink roller andreducing the load on the endless printing bands 7.

Further, since an attempt to rotate a selector wheel from itsrotation-prevented state causes it to rotate idly owing to separationbetween the outer peripheral surface of the selector wheel in thedirection of rotation and the inner peripheral surface of the endlessprinting band, no load arises owing to contact friction between the twosurfaces.

When the tension adjustment mechanism is provided within the endlessprinting bands, moreover, the degree of endless printing band tensioningcan be simply adjusted by rotating the adjuster within a prescribedrange.

We claim:
 1. A printing apparatus having at least one endless printingband formed on its outer peripheral surface with multiple types anddisplay characters and wound about a selector wheel and a type bearingmember section and enabling selection of a desired type of the endlessprinting band,a movable stop member provided between the selector wheeland the type bearing member section and having one end portion formedwith at least one regulating boss portion for engaging the selectorwheel and having at another end portion formed with an elastic sectionhaving at least one engagement piece, a stop bearing member forrestricting movement of the movable stop member by abutting on theelastic section of the movable stop member, and at least one driveprojection provided on an inner peripheral surface of the endlessprinting band to be engageable with the engagement piece of the elasticsection of the movable stop member, engagement between the driveprojection and the engagement piece with movement of the endlessprinting band causing movement of the movable stop member to enablerelease of the engagement between the selector wheel and the regulatingboss section.
 2. The printing apparatus of claim 1 further comprising astop guide for guiding the movable stop member in its movementdirection.
 3. The printing apparatus of claim 1, wherein the elasticsection has a bifurcated engagement spring section.
 4. The printingapparatus of claim 1, wherein the stop bearing member has a slantedsurface for bearing the elastic section.
 5. The printing apparatus ofclaim 1, wherein the inner peripheral surface of the endless printingband is formed with at least one drive projection at a portion oppositea display character and is made flat at a portion opposite a type. 6.The printing apparatus of claim 1, wherein the outer peripheral surfaceof the endless printing band is formed with at least one blank sectionwith no types and the inner peripheral surface opposite at least onedisplay character adjacent to a side of the blank section in thedirection of rotation is made a flat section.
 7. The printing apparatusof claim 1, further comprising a cam member whose rotational positioncan be adjusted is provided within the endless printing band to berotatable into and out of contact with the inner peripheral surface ofthe endless printing band.
 8. The printing apparatus of claim 7, whereinthe cam member has a cam adjustment rotary shaft and an adjustment armperpendicular to the cam adjustment rotary shaft.
 9. The printingapparatus of claim 7, further comprising a printer frame on which theselector wheel and the type bearing member section are provided, theprinter frame having an adjustment groove section enabling adjustment ofthe rotational position of the cam member.
 10. The printing apparatus ofclaim 7, wherein the cam member is sectionally elliptical.
 11. Aprinting apparatus having at least one endless printing band formed onits outer peripheral surface with multiple types and display charactersand wound about a selector wheel and a type bearing member section andenabling selection of a desired type of the endless printing band,a stopmember provided between the selector wheel and the type bearing memberselection and at least one drive projection provided on an innerperipheral surface of the endless printing band to be engageable withthe stop member, engagement between the drive projection and the stopmember with movement of the endless printing band producing slack in theendless printing band to enable idle rotation of the selector wheel, acam member within the endless printing band, the cam member having arotational position which can be adjusted within endless printing bandto be rotatable into and out of contact with the inner peripheralsurface of the endless printing band.
 12. The printing apparatus ofclaim 11, wherein the cam member is sectionally elliptical.
 13. Theprinting apparatus of claim 11, wherein the cam member has a camadjustment rotary shaft and an adjustment arm perpendicular to the camadjustment rotary shaft.
 14. The printing apparatus of claim 11, furthercomprising a printer frame on which the selector wheel and the typebearing member section are provided is formed with an adjustment groovesection enabling adjustment of the rotational position of the cammember.